To produce maple syrup, the sugar content of maple sap, which can be between 1 and 3° Brix at the time of harvesting for instance, must be brought to a much higher (denser) concentration, typically around 65-70° Brix. Traditionally, this was entirely done through evaporation. FIG. 1 shows a typical prior art evaporator 10 including two evaporation stages 14, 16, both positioned above a combustion chamber 12 to receive heat from combusting wood or the like. The first evaporation stage 14, commonly referred to as a folded pan 14a, or flue pan, had an increased area of heat transfer due to the presence of folds 18, and was used to bring the sugar content to about 45° Brix in a reasonable amount of time. The second evaporating stage 16, commonly referred to as a flat pan 16a, was used subsequently to the folded pan 14a for the delicate final stage of transforming the concentrated maple sap into maple syrup without burning it, during which stage the sugar content was raised from ˜45° Brix to ˜65-70° Brix. It will be understood that evaporating requires a substantial amount of energy, usually obtained from the combustion of wood or oil, and which is reflected in the final cost of maple syrup.
In an effort to reduce the energy and costs associated to evaporation, a reverse osmosis stage 20 has been introduced upstream of the folded pan 14a. Essentially, reverse osmosis uses at least one separator 22 provided in the form of a pressure-resistant housing 24 (often cylindrical) containing a selective membrane 26. Fresh maple sap is fed into the separator 22 under pressure, and water, referred to as a filtrate 28, is extracted from the maple sap across the membrane 26, thereby yielding maple sap to a higher degree of concentration (typically between 13 to 20° Brix nowadays) prior to evaporation. The concentrated maple sap is then fed to the folded pan 14a where it can be concentrated to around 45° Brix using a significantly lesser amount of energy. The reduction of energy consumption does not only come from the fact that the maple sap fed into the evaporator 10 is already closer to the desired density, but also from the fact that the significant amount of water filtrate 28, which is extracted during reverse osmosis, significantly reduces the volume of sap entering the evaporator, thereby reducing the volume of sap which requires to be evaporated.
Notwithstanding the apparent advantages, it took several years for the use of reverse osmosis to become widespread. Maple syrup producers feared that its presence in the process would affect the taste, color, or overall quality of the final maple syrup product. Today, it is generally accepted to concentrate the maple sap to between 13 and 20° Brix using a reverse osmosis separator at a pressure between 300-500 psi prior to evaporation, and many industrial production plants are so equipped. Typically, the pressure is maintained by a combination of a pump 32 provided upstream of the membrane 26, and a valve 34 positioned in the concentrate outlet line, prior to releasing the concentrate to atmospheric pressure. A recirculation pump 30 is typically used to artificially increase the flow rate of maple sap across the separator 22 to increase the overall flow rate of production. The filtrate 28, which may still contain a low concentration of sugar, is disposed of.
Although energy saving considerations provide an incentive to increase the maple sap concentration even more prior to evaporation, attempting to do so faced those who tried to challenges which remain unaddressed. Henceforth, although the introduction of the afore-mentioned technology has represented a significant advancement in the production of maple syrup, there remained room for improvement.